The invention relates to a thermoplastic/elastomer composite product such as, for example, a hose for transporting a coolant for an automobile air-conditioning circuit.
These products must meet increasingly stringent standards, especially with regard to their thermal behavior (both internal and external), their resistance to external agents and, when they are hoses, their impermeability with respect to the fluid transported. In addition, their lifetime must be as long as possible and their sealing and impermeability properties must be maintained throughout this lifetime.
It has been proposed many times to produce thermoplastic/elastomer composite hoses for transporting fluids in the automobile industry, these hoses generally having an internal layer of polyamide, an elastomer layer covering the polyamide, a textile reinforcement and an external protective layer made of rubber or elastomer.
In these known hoses, it is often necessary to make a compromise between the desired flexibility and the impermeability to the fluid transported and a thin layer of a suitable adhesive material must furthermore be placed between the thermoplastic and the elastomer in order ensure that they adhere to each other.
In the case of hoses for transporting the coolant for an air-conditioning circuit, it is necessary to improve the impermeability to the fluid transported (the coolants which have been used hitherto and contained CFCs are being replaced by HFCs known by the name R134a, these being combined with a lubricant of the polyalkylene glycol type) and a blend of a polyamide, of a polyolefin modified by grafting and of xcex5-caprolactam has, for example, been proposed for this internal layer, but this composition does not adhere to the layer of elastomer that covers it. In addition, the amount of xcex5-caprolactam used is a compromise between flexibility and fluid impermeability, the addition of xcex5-caprolactam making it possible to improve the flexibility to the detriment of the impermeability.
This is why the Applicant gave itself the task of providing a composite product which meets the practical requirements better, especially in that there is complete adhesion between the thermoplastic and the elastomer as well as excellent impermeability to the fluids transported (in the case of a hose) and especially to the new coolants which are used in automobile air-conditioning circuits.
For this purpose, the invention proposes a composite product comprising an internal layer of a blend of a thermoplastic and of a modifier, said layer being covered with a layer of a blend of an elastomer and of a modifier, wherein:
the internal layer essentially consists of a plastic alloy comprising a thermoplastic chosen from among polyamides (PA) and at least one modifier chosen from among ethylene-acrylate-acrylic acid terpolymers, the thermoplastic/ethylene-acrylate-acrylic acid terpolymer proportions being between 10/90 and 49/51 (by weight); and
the elastomer is chosen from among natural rubber (polyisoprene or NR), synthetic polyisoprene (IR), nitrile rubbers (NBR), halogenated nitrile rubbers, hydrogenated nitrile rubbers, epichlorhydrin-ethylene oxide copolymers (ECO), ethylene-acrylic acid elastomers, butyl rubbers (isoprene-isobutylene copolymers or IIR), halogenated butyl rubbers (XIIR), isobutylene-p-methylstyrene para-bromomethylstyrene elastomers, ethylene-propylene-diene terpolymers (EPDM) and ethylene-propylene copolymers (EPM), chlorinated polyethylene (CM), chlorosulfonated polyethylene (CSM), chlorosulfonated polyethylene having alkyl side groups (ACSM), polychloroprene (CR), acrylic polymers (ACM), ethylene-vinyl acetate copolymers (EVA) and ethylene-acrylate copolymers (EAM), at least one modifier, which modifies the elastomer, being chosen from among 1,2-vinyl polybutadienes grafted with maleic anhydride, epoxidized and/or hydroxylated polybutadienes, silanes, ethylene-acrylic acid elastomers and ethylene-propylene copolymers grafted with maleic anhydride.
According to the invention, the polyamide is selected from the group consisting, inter alia, of nylon-6, nylon-6,6, nylon-11, nylon-12, nylon-6/10 and nylon-6/12.
It has been found that, in these products, there is complete adhesion between the thermoplastic and the elastomer without it being necessary to use an interlayer of an adhesive, and that it is impossible to separate the thermoplastic and elastomer layers without destroying them.
It has also been found that insofar as the proportions of modifiers in the thermoplastic are always greater than the amounts of thermoplastic, they form with the latter a plastic alloy whose manufacture is significantly improved insofar as it is possible to obtain a much more homogeneous dispersion than those obtained with the modified thermoplastics of the prior art, in which the amounts of modifiers are generally less than those of the thermoplastic; such a homogeneous dispersion makes it possible, in particular, to obtain components of very high quality manufactured by extrusion, the elastomer and/or the thermoplastic advantageously including several modifiers.
The proportions of modifiers in the elastomer may vary very widely and are, in general, between 0.5 and 50% approximately.
The thermoplastic and/or the elastomer used may also include at least fillers, either organic or inorganic, as well as the usual plasticizers.
The invention also proposes a hose for transporting a coolant for an automobile air-conditioning circuit, comprising an internal layer of the thermoplastic and a layer of the elastomer which have just been described, in which hose the thickness of the internal layer of thermoplastic is approximately 0.05 to 2 mm, that of the layer of elastomer being approximately 0.2 to 3 mm.
Such a hose also includes one or more textile reinforcement layers covering the layer of elastomer and itself covered with a protective layer made of elastomer.
A thin layer of elastomer may also be provided on the internal face of the layer of thermoplastic, in order to improve the sealing when the hose is fitted onto a connection nozzle.
In a preferred embodiment of the invention, the aforementioned thermoplastic is a blend of 35 to 45% (w/w) of polyamide, preferably nylon-6, and of 55 to 65% (w/w) of an ethylene-acrylate-acrylic acid terpolymer.